XRT74L73 Datasheet, PDF (290/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
TABLE 62: LISTING AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE TRANSMIT PAYLOAD DATA INPUT
INTERFACE
SIGNAL NAME
TxSer
TxNib[2:0]
TxInClk
TxNibClk
TxOHInd
TxFrame
TxFrameRef
RxOutClk
TYPE
DESCRIPTION
Input
Input
Input
Transmit Serial Payload Data Input Pin:
If the user opts to operate the XRT74L73 in the serial mode, then the Terminal Equipment is
expected to apply the payload data (that is to be transported via the outbound E3 data stream)
to this input pin. The XRT74L73 will sample the data that is at this input pin upon the rising
edge either the RxOutClk or the TxInClk signal (whichever is appropriate).
NOTE: This signal is only active if the NibInt input pin is pulled "Low".
Transmit Nibble-Parallel Payload Data Input pins:
If the user opts to operate the XRT74L73 in the Nibble-Parallel mode, then the Terminal Equip-
ment is expected to apply the payload data (that is to be transported via the outbound E3 data
stream) to these input pins. The XRT74L73 will sample the data that is at these input pins
upon the rising edge of the TxNibClk signal.
NOTE: These pins are only active if the NibInt input pin is pulled "High".
Transmit Section Timing Reference Clock Input pin:
The Transmit Section of the XRT74L73 can be configured to use this clock signal as the Tim-
ing Reference. If the user has made this configuration selection, then the XRT74L73 will use
this clock signal to sample the data on the TxSer input pin.
NOTE: If this configuration is selected, then a 34.368 MHz clock signal must be applied to this
input pin.
Output ^{Transmit Nibble Mode Output}
If the user opts to operate the XRT74L73 in the Nibble-Parallel mode, then the XRT74L73 will
derive this clock signal from the selected Timing Reference for the Transmit Section of the chip
(e.g., either the TxInClk or the RxLineClk signals).
The XRT74L73 will use this signal to sample the data on the TxNib[2:0] input pins.
Output ^{Transmit Overhead Bit Indicator Output:}
This output pin will pulse "High" one-bit period prior to the time that the Transmit Section of the
XRT74L73 will be processing an Overhead bit. The purpose of this output pin is to warn the
Terminal Equipment that, during the very next bit-period, the XRT74L73 is going to be process-
ing an Overhead bit and will be ignoring any data that is applied to the TxSer input pin.
Output ^{Transmit End of Frame Output Indicator:}
The Transmit Section of the XRT74L73 will pulse this output pin "High" (for one bit-period),
when the Transmit Payload Data Input Interface is processing the last bit of a given E3 frame.
The purpose of this output pin is to alert the Terminal Equipment that it needs to begin trans-
mission of a new E3 frame to the XRT74L73 (e.g., to permit the XRT74L73 to maintain Trans-
mit E3 framing alignment control over the Terminal Equipment).
Input
Transmit Frame Reference Input:
The XRT74L73 permits the user to configure the Transmit Section to use this input pin as a
frame reference. If the user makes this configuration selection, then the Transmit Section will
initiate its transmission of a new E3 frame, upon the rising edge of this signal.
The purpose of this input pin is to permit the Terminal Equipment to maintain Transmit E3
Framing alignment control over the XRT74L73.
Output ^{Loop-Timed Timing Reference Clock Output pin:}
The Transmit Section of the XRT74L73 can be configured to use the RxLineClk signal as the
Timing Reference (e.g., loop-timing). If the user has made this configuration selection, then
the XRT74L73 will:
• Output a 34.368 MHz clock signal via this pin, to the Terminal Equipment.
• Sample the data on the TxSer input pin, upon the rising edge of this clock signal.
Operation of the Transmit Payload Data Input In-
terface
The Transmit Terminal Input Interface is extremely
flexible, in that it permits the user to make the follow-
ing configuration options.
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